1. Field of the Invention
The invention relates to a doctor blade and to a method for producing doctor blades from metal, the doctor blades to be produced having a reduced material thickness in a region of a working edge, the material thickness being essentially constant in this region.
2. Description of the Related Art
Doctor blades serve for distributing and wiping off liquid and pasty masses. They are used, inter alia, in packaging intaglio printing, illustrative and decorative intaglio printing, flexographic printing, UV flexographic printing, aniloxoffset, pad printing and rotary screenprinting, and also in coating methods. For example, in intaglio printing, the excess printing ink is wiped off from the bridges of the impression cylinder by means of a doctor blade in the region of a working edge, so that only the wells are filled with ink (scraping off). By contrast, in screenprinting, the doctor blade is used in order to press the printing ink through the orifices in the screen on to the print carrier. The doctor blade may be designed as a steel strip ground in the manner of a knife, but doctor blades made from plastic or composite materials are also known.
Doctor blades may be subdivided essentially into three groups on the basis of their cross-sectional profile:
1. Doctor blades of wedge form (wedge doctor blades) have a cross-sectional area in the form of a trapezium with two right angles. The working edge may in this case also be flattened or rounded.
2. Doctor blades with round edges have essentially a cross-sectional area in the form of a rectangle, the working edge being rounded.
3. Doctor blades with lamellae (lamellar doctor blades) have a cross-sectional area in the form of a rectangle with a cutout which is essentially rectangular and emanates from one corner, in which case the concave region of the lamellar doctor blade may be rounded and a working edge is usually rounded.
The profiling in lamellar doctor blades is typically achieved by means of a grinding operation, in which a cutting movement is generated as a result of a rotation of a cutting tool with respect to the chucked workpiece. The milling operation is followed by a remachining of the main surfaces, in order to eliminate the unevenesses which have arisen due to the milling operation. Remachining typically takes place by means of a polishing operation and/or lapping operation.
GB 1,289,609 relates to wear-resistant doctor blades. These comprise regions consisting of a hard material and regions consisting of a soft material. The metal doctor blade has on one side surface a long, flat and narrow recess which runs parallel to the working edge. The recess holds a strip of wear-resistant material, the hardness of which is higher than that of the surrounding material. The recess may be produced by planing, milling, grinding or forming.
US 2008/0096037 A1 relates to a steel strip for the production of doctor blades, the steel used having a composition of 1-3% by weight C, 4-10% by weight Cr, 1-8% by weight Mo, 2.5-10% by weight V and otherwise iron, and the steel strip being produced by means of a powder-metallurgical method. In the production of the doctor blades, the edges of the strip may be machined by planing and/or milling in order to obtain the desired edge profile.
DE-A 1 807 325 relates to a non-generic method for the production of doctor blades (in particular, paper-coating knives), which refers to doctor blades of wedge form. Their oblique surface is produced by planing in the longitudinal direction of the doctor blade. A better smoothness is thereby to be achieved, while at the same time the production costs can be lowered, as compared with conventional doctor blades which are machined by grinding and honing. It is especially important, according to the publication, that transverse grooves in the region of the working edge can be avoided by means of the planing. Preferably, machining by planing is carried out, with a single chip being lifted off, using a single hard-metal planing chisel. The surfaces adjacent to the oblique surface are also preferably machined in the longitudinal direction.
The known methods for the production of lamellar doctor blades having a region with a constantly reduced material thickness are slow and complicated.
What is needed, therefore, is an improved doctor blade and method and system for producing doctor blades.